Siriraj Hospital is the Thailand’s largest university-based national tertiary referral center. This study was conducted at Siriraj Hospital, Mahidol University, Bangkok, Thailand. Follow-up data were also extracted for the average of 3.53 ± 1.27 years. This is a retrospective cohort study design. Accordingly, the aim of this study was to identify the optimal INR level for warfarin therapy after mechanical mitral valve replacement in Thai patients. However, the currently available data from Thai population are insufficient for defining the optimal INR level for anticoagulant therapy in Thai mechanical valve recipients. The few studies that were conducted in Asian populations who received mechanical heart valve replacement generally recommended a lower INR level as being appropriate for anticoagulant therapy. There is no clear explanation for the increased risk of intracerebral bleeding in Asian population. Asian population had a greater proportion of intracerebral bleeding as a stroke subtype when compared to Caucasians. Previous data have shown that Asian population with atrial fibrillation who received warfarin has an increased risk of intracranial hemorrhage up to 4 times compared to Caucasians. These data were based on results from studies conducted in Western countries however and according to our review of the literature, data regarding the safety of warfarin in Asian populations remain insufficient. A target INR range of 2.5–3.5 is the current recommendation in patients who have undergone mechanical mitral valve replacement. Current American and European clinical guidelines recommend a higher international normalized ratio (INR) for anticoagulant therapy after mechanical mitral valve replacement, because higher rates of thromboembolic complications were reported when the mechanical valve was in the mitral position, as compared to when the mechanical valve was in the aortic position. Risk of thromboembolism and bleeding is commensurate with the level of anticoagulation. However, bleeding complications that result from excess dose of anticoagulants adversely impacts patients’ quality of life and can cause unnecessary morbidity and mortality. Lifelong oral anticoagulation therapy for prevention of thromboembolic events is recommended in all patients who undergo mechanical heart valve replacement.

The optimal INR level was within the range of 2.0 to 3.4 in our cohort of Thai mechanical mitral valve replacement patients. Statistically significant differences were observed between INR 2.3 to 4 and 3.4 ( p < 0.001). The overall event rate was lowest in the 2.0 to 3.4 INR range. The percentage of patient time spent within INR 2.5–3.4, INR 3.4 was 41.96, 54.04, and 4%, respectively. Intracranial bleeding occurred in 3 patients (2.62 per 100 patient-years). Eleven patients experienced 13 thromboembolic events (3.42 per 100 patient-years), and 12 patients experienced 18 total bleeding events (5.50 per 100 patient-years). Mean duration of follow-up was 3.53 ± 1.27 years. Two hundred patients were included and followed over a period of 707.81 patient-years. The optimal INR level was defined as the level with the lowest incidence density of thromboembolic or hemorrhagic complications. INR range was classified into 6 groups ( 4.5). We retrospectively reviewed the medical records of mechanical mitral valve replacement patients who received warfarin therapy at Siriraj Hospital. Data are scarce regarding the optimal international normalized ratio (INR) in Thai patients who require warfarin therapy after mechanical mitral valve replacement.

Warfarin inr normal range